The smallest named unit in the metric system is the yoctogram, equal to 0.000000000000000000000001 grams. (Yes, that’s 24 zeros.) For a scale that can measure differences in mass as small as a yoctogram, which is on the order of the mass of a proton, physicists writing in Nature Nanotechnology turned to the wunderkind of nanotechnology: carbon nanotubes.

Carbon nanotubes are tiny—though not quite yoctogram-tiny—sheets of carbon rolled up into a cylinder. When an atom or molecule is placed on a vibrating carbon nanotube, the nanotube’s resonance frequency changes depending on the molecule’s mass. The sensor works at temperatures below -200 Celsius and in a vacuum, which eliminates the possibility of gas molecules bouncing around and messing with measurements.